The Multimedia Broadcast Multicast Service (MBMS) is a point-to-multipoint service, which is designed to provide efficient delivery of broadcast and multicast services. Specifically, multicast and broadcast content may be transmitted from a single source entity to multiple recipients.
MBMS may be considered a key new feature of the Long Term Evolution (LTE) project, which focuses on enhancing the Universal Terrestrial Radio Access Network (UTRAN). MBMS exploits the LTE radio interface to transmit multicast or broadcast data as a multi-cell transmission over a synchronized Single Frequency Network (SFN). Such an operation may be known as a MBMS over Single Frequency Network (MBSFN) and operates by making the MBSFN transmission appear to the wireless devices receiving the transmission as if the transmission is from a single larger cell.
MBMS may be is split into the MBMS Bearer Service and the MBMS User Service. The MBMS Bearer Service includes a Multicast- and a Broadcast Mode with only the Broadcast mode being available over LTE. MBMS Bearer Service uses IP multicast addresses for the delivery of content. The advantage of the MBMS Bearer Service compared to unicast bearer services includes the sharing of transmission resources in the core and radio networks. For example, MBMS may use an advanced counting scheme to decide, whether or not zero, one or more dedicated (i.e. unicast) radio channels lead to a more efficient system usage than one common (i.e. broadcast) radio channel. The MBMS User Service is basically the MBMS Service Layer and offers a Streaming- and a Download Delivery Method. The Streaming Delivery method can be used for continuous transmissions like Mobile TV services. The Download Method is intended for “Download and Play” services.
Evolved MBMS (eMBMS) is an emerging technology for LTE that allows efficient distribution of live and premium content to subscribers. Specifically, eMBMS is a highly efficient means of broadcasting content to multiple users simultaneously, utilizing LTE networks. This emerging broadcast technology for LTE has the potential to greatly reduce the cost for distribution of popular multimedia content—both for streaming as well as for content delivered during off-peak hours, stored in mobile device memory, and accessed at a time of the user's choosing. eMBMS may be particularly useful during live events, such as music concerts or sports events, where millions of consumers are simultaneously viewing the same content, and where eMBMS could be used to broadcast complementary content, like different camera angles for instance, to users of LTE devices.
By introducing eMBMS, operators can make better use of their available spectrum and free up network capacity. In this way, operators will be able to maximize efficiency when offering services such as live TV, video on demand, podcasts and even software upgrades to a large number of mobile devices and set-top boxes. However, such services are not without their limitations. On such limitation may be reliability where the content is transmitted to many different devices in differing areas and sub-areas of a service area. However, there are ways to improve reliability. One such method that operates efficiently for unicast transmission is the Automatic Repeat re-Quest (ARQ). However, in a multicast transmission scheme, a feedback implosion problem may occur when too many receivers are transmitting back to the sender at one time.
To increase transmission reliability in MBMS and eMBMS contexts, an application layer forward error correction (FEC) code may be used. Using an FEC scheme, the sender of the multicast or broadcast content adds redundant information in the messages transmitted to the receivers. The redundant information allows the receiver to reconstruct the source data. While such schemes may improve reliability, they inevitably add a constant overhead in the transmitted data and are computationally expensive at the receiver. Additionally, it may be very difficult for the operator to decide how much redundant information should be added so that all wireless devices receiving MBMS services receive acceptable quality of service (QoS).
Furthermore, eMBMS uses fixed content bit rates and coding rates that are tuned for the wireless devices experiencing the worst channel conditions. To ensure that these wireless devices receive adequate services, the network may over-provision resources for certain sub areas. Additionally, the conventional eMBMS does not provide QOS differentiated services.